Character type vertical alignment mode liquid crystal display device with wall layers

ABSTRACT

In a character type vertical alignment type liquid crystal display device including first and second substrates opposing each other, a first electrode layer including a plurality of first electrodes provided at an inner side of the first substrate, a second electrode layer including a plurality of second electrodes provided at an inner side of the second substrate, and a vertical alignment mode liquid crystal layer provided between the first and second substrates, a wall structure is provided between the first and second substrates.

This is a Continuation of U.S. application Ser. No. 12/617,918, filedNov. 13, 2009, which claims the benefit of priority under 35 U. S. C.§119 from prior Japanese Patent Application Nos. JP2008-308354 andJP2008-309532, filed Dec. 3, 2008 and Dec. 4, 2008, respectively, theentire contents of all of which are incorporated herein by reference.

BACKGROUND

1. Field

The presently disclosed subject matter relates to a character typevertical alignment mode liquid crystal display (LCD) device.

2. Description of the Related Art

In a prior art character type vertical alignment mode LCD device, sinceliquid crystal molecules are vertically aligned with respect tosubstrates while applying no voltage thereto, the black representationis excellent. Also, when an optical compensation plate or a retardationfilm having a negative optical isomer property is introduced onto one orboth polarizers, the viewing angle properties are very excellent (see:JP2005-234254A).

Also, a rubbing aligning process or an ultraviolet ray aligning processis performed upon alignment layers, to thereby realize a mono-domainalignment in a vertical alignment mode liquid crystal layer. On theother hand, slits are provided on electrode layers or ridges areprovided on substrates, to thereby realize a multi-domain alignment in avertical alignment mode liquid crystal layer. Particularly, theabove-mentioned mono-domain aligning process can make the alignmentstate of the vertical alignment mode liquid crystal layer uniformregardless of whether or not a voltage is applied thereto.

Further, in order to avoid alignment defects in the vertical alignmentmode liquid crystal layer while applying a voltage thereto, a pretiltangle is allocated so that liquid crystal molecules in the verticalalignment mode liquid crystal layer are tilted a little from a verticalangle (90°) with respect to the substrates while applying no voltagethereto.

In the above-described prior art character type vertical alignment modeLCD device without requiring thin film transistors (TFTs), amultiplexing driving is used. A typical multiplexing driving is based onan optimal bias method whose driving waveforms are an in-frame-reversaldriving waveform or a line-reversal driving waveform (hereinafter,referred to as an A-waveform), a frame-reversal driving waveform(hereinafter, referred to as a B-waveform), and a multi-line-reversaldriving waveform (hereinafter, referred to as a C-waveform). Note thatthe B-waveform is now often used in view of the small power consumption.

In the above-described prior art character type vertical alignment modeLCD device, however, since the anchoring force of the direction of theazimuth of liquid crystal on the plane of the substrates is weaker thanthat of a horizontal alignment mode LCD device such as a twistednematic-mode (TN-mode) LCD device, when the direction of the azimuth ofliquid crystal on the plane of the substrates is deviated by someexternal factors from a direction set by an alignment process, theretardation would be partly changed, so that a low transmittivity regionwould be visible as a “black shadow region” within a white pixel (dot)of the vertical alignment mode liquid crystal layer while applying avoltage thereto. Also, if the viewing angle is changed, the black shadowregion would be visible as a “rough region”. Further, if one blackshadow region within one white dot reaches another black shadow regionof its adjacent white dot, a plurality of black shadow regions arevisible as an “irregularly-continuous region” within continuous whitedots. The phenomenon of such a black shadow region, a rough region andan irregularly-continuous region is called a dynamic misalignment (DMA)phenomenon which would not only decrease the uniformity ofrepresentation of dots, but would erase patterns represented by dots.

The generation state of the above-mentioned DMA phenomenon may bechanged due to various internal factors such as a pretilt angleaffecting the anchoring force of the azimuth of the direction of liquidcrystal on the plane of the substrates and the frame response phenomenonof liquid crystal.

Also, the generation state of the above-mentioned DMA phenomenon may bechanged due to some external factors. One of the external factors is anoblique electric field generated between electrode layers, i.e., asegment electrode layer and a common electrode layer. In more detail, anoblique electric field is generated between an edge of one segmentelectrode of the segment electrode layer and an even portion of onecommon electrode of the common electrode layer. Similarly, an obliqueelectric field is generated between an edge of one common electrode ofthe common electrode layer and an even portion of one segment electrodeof the segment electrode layer. Particularly, the generation state ofthe DMA phenomenon in the vertical alignment mode LCD device is stronglyaffected by the above-mentioned oblique electric field. That is, sincethe liquid crystal in the vertical alignment mode LCD device is of anegative type, the director of liquid crystal can easily fall along adirection perpendicular to an electric line of force of an electricfield applied thereto, so that the director of liquid crystal easilyfalls along a direction perpendicular to an electric line of force ofthe above-mentioned fringe field. Therefore, if the director of liquidcrystal is different from a director of liquid crystal set by analignment process, a black shadow region would be visible between theboundaries of the segment and common electrodes.

In the above-described prior art character type vertical alignment modeLCD device, since the pretilt angle is around 90° so that the anchoringforce of liquid crystal along the direction of the azimuth thereof onthe plane of the substrates is very small, and also, the liquid crystalis in a high response speed state, the liquid crystal is easily movedalong the direction of the azimuth thereof on the plane of thesubstrates. That is, the above-mentioned high pretilt angle is requiredto improve the sharpness for high viewing angle properties at a highduty ratio driving operation. Also, the above-mentioned high responsespeed state can be realized by the low viscosity of liquid crystal, athin thickness of a liquid crystal layer, a high operational temperatureand so on. As a result, a director of liquid crystal would be generatedfrom a start position where an oblique electric field whose direction isdifferent from the direction of the azimuth of liquid crystal set by thealignment process is generated along a direction different from thedirection of azimuth of liquid crystal set by an alignment process. Inthis case, since liquid crystal molecules have forces to make themparallel with each other, and the anchoring force of liquid crystalalong the direction of the azimuth thereof on the plane of thesubstrates is very small, as stated above, a black shadow region withdeviated directors of liquid crystal is spread gradually from theabove-mentioned start position to its peripheral positions. Thus, alarge number of directors of liquid crystal are deviated from thealignment direction set by the alignment process.

In order to avoid the generation of the above-mentioned black shadowregion, one approach is to suppress the frame response phenomenon. Thatis, a high frequency driving method increasing the frame frequency andusing the A-waveform, the C-waveform or a multi-line addressing (MLA)waveform is carried out to decrease a pulse interval by a multiplexingdriving. However, this high frequency driving method would increase thepower consumption and also, would increase the crosstalk phenomenon byresistance components of the electrode layers.

SUMMARY

The presently disclosed subject matter seeks to solve one or more of theabove-described problems.

According to the presently disclosed subject matter, in a character typevertical alignment mode LCD device including first and second substratesopposing each other, a first electrode layer including a plurality offirst electrodes provided at an inner side of the first substrate, asecond electrode layer including a plurality of second electrodesprovided at an inner side of the second substrate, and a verticalalignment mode liquid crystal layer provided between the first andsecond substrates, a wall structure is provided between the first andsecond substrates.

The wall structure comprises a grid-shaped wall layer.

Generally, in a character type vertical alignment mode LCD device, sincedisplay patterns formed by straight lines and curves have complexshapes, the relationship between an oblique electric field caused by anedge of an electrode and an even portion of another electrode and thedirector of liquid crystal caused by a pretilt angle is more complexthan that of a dot-matrix vertical alignment LCD device, so that the DMAphenomenon is easily generated. On the other hand, the DMA phenomenonhas liquid properties. Therefore, the inventor has found the grid-shapedwall layer to suppress the propagation of liquid crystal along alldirections, thus suppressing the propagation of the DMA phenomenon.

Also, the wall structure has wall layers each with a shape along aperiphery of one of display patterns formed by superposing the segmentelectrodes onto the common electrodes.

Further, the wall structure has additional wall layers having reducedshapes of the wall layers.

The above-mentioned wall layers and additional wall layers suppress thegeneration of the detector of liquid crystal by the mutual alignmentability of liquid crystal modules, thus suppressing the propagation ofthe DMA phenomenon.

According to the presently disclosed subject matter, the propagation ofthe DMA phenomenon can be suppressed. Also, since a high frequencydriving is unnecessary, the power consumption can be decreased and also,the crosstalk can be decreased. Further, since the DMA phenomenon in ahigh temperature region can be decreased, the operational margin can bebroadened. Furthermore, since the pretilt angle can be increased, thesharpness, i.e., the contrast can be improved and, also, the viewingangle properties can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of the presently disclosedsubject matter will be more apparent from the following description ofcertain embodiments, as compared with the prior art, taken inconjunction with the accompanying drawings, wherein:

FIG. 1 is a layout diagram illustrating segment electrodes of a priorart character type vertical alignment mode LCD device;

FIG. 2 is a layout diagram illustrating common electrodes of the priorart character type vertical alignment mode LCD device;

FIG. 3 is a layout diagram of display patterns of the prior artcharacter type vertical alignment mode LCD device by superposing thesegment electrodes of FIG. 1 onto the common electrodes of FIG. 2;

FIG. 4 is a layout diagram illustrating a first embodiment of thecharacter type vertical alignment mode LCD device according to thepresently disclosed subject matter;

FIG. 5 is a layout diagram illustrating a modification of the charactertype vertical alignment mode LCD device of FIG. 4;

FIG. 6 is a cross-sectional view of the character type verticalalignment mode LCD device of FIG. 4 or 5;

FIGS. 7 and 8 are microscopic picture diagrams for explaining theexperimental results obtained by driving the character type verticalalignment mode LCD device of FIG. 6;

FIGS. 9 and 10 are cross-sectional views illustrating modifications ofthe character type vertical alignment mode LCD device of FIG. 6;

FIG. 11 is a layout diagram illustrating a second embodiment of thecharacter type vertical alignment mode LCD device according to thepresently disclosed subject matter;

FIG. 12 is a cross-sectional view of the character type verticalalignment mode LCD device of FIG. 11;

FIG. 13 is a microscopic picture diagram illustrating a first example ofthe wall layers of FIG. 11;

FIG. 14 is a microscopic picture diagram illustrating a second exampleof the wall layers of FIG. 11;

FIGS. 15 and 16 are microscopic picture diagrams for explaining theexperimental results obtained by driving the character type verticalalignment mode LCD device of FIG. 11;

FIG. 17 is a layout diagram illustrating a modification of the charactertype vertical alignment mode LCD device of FIG. 11;

FIG. 18 is a cross-sectional view of the character type verticalalignment mode LCD device of FIG. 17; and

FIGS. 19 and 20 are cross-sectional views illustrating modifications ofthe character type vertical alignment mode LCD device of FIG. 12.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before the description of exemplary embodiments, a prior art charactertype vertical alignment mode LCD device will now be explained withreference to FIGS. 1, 2 and 3.

In FIG. 1, segment electrodes SEG1, SEG2, . . . , SEG13 are provided.Also, in FIG. 2, common electrodes COM1, COM2, . . . , COM6 areprovided. Further, in FIG. 3, display patterns are provided. In thiscase, the display patterns of FIG. 3 are realized by superposing thesegment electrodes SEG1, SEG2, . . . , SEG13 of FIG. 1 onto the commonelectrodes COM1, COM2, . . . , COM6 of FIG. 2.

The display patterns of FIG. 3 are divided into a small-sized pattern P1and a large-sized pattern P2. The small-sized pattern P1 has aline-width of about 0.4 mm (400 μm), and the large-sized pattern P2 hasa line-width of about 0.8 mm (800 μm).

In FIG. 4, which illustrates a first embodiment of the character typevertical alignment mode LCD device according to the present invention, agrid-shaped wall layer W1 is added to the elements of the prior artcharacter type vertical alignment mode LCD device of FIGS. 1, 2 and 3.In FIG. 4, note that the display patterns of FIG. 3 are illustrated, butthe segment electrodes SEG1, SEG2, . . . , SEG13 of FIG. 1 and thecommon electrodes COM1, COM2, . . . , COM6 of FIG. 2 are omitted.

As illustrated in FIG. 4, assume that the right direction viewed fromthe top is 0°, the upper direction is 90°, the left direction is 180°,and the lower direction is 270°, the reference angle of the grid-shapedwall layer W1 is 0°. In this case, the grid-shaped wall layer W1 has norelation to the display patterns. Even when the reference angle of thegrid-shaped wall layer W1 is an arbitrary angle deviated from 0°, thesuppressing effect of the propagation of the DMA phenomenon isunchanged. Particularly, when the grid-shaped wall layer W1 interfereswith a light output distribution due to the structure of a backlightguide plate such as the prism thereof to generate moiré fringes, thereference angle of the grid-shaped wall layer W1 can be deviated alittle from 0° to suppress the moiré fringes.

In FIG. 5, which illustrates a modification of the character typevertical alignment mode LCD device of FIG. 4, the reference angle of thegrid-shaped wall layer W1 is 45°. In this case, polarizers (see 11 and21 of FIG. 6) cross at 90°, and the polarizing angles of the polarizersare +45° and −45° (315°), respectively. That is, the refractive index ofthe grid-shaped wall layer W1 is generally different from that of liquidcrystal, so that a light penetration state may be established due to thedifferent compensation conditions viewed from the oblique side. Thus,the black representation may deteriorate. In order to improve the blackrepresentation in such a state, the reference angle of the grid-shapedwall layer W1 coincides with one of the polarizing angles of thepolarizers, i. e., 45°, thus improving the visibility of all the displaypatterns.

Referring to FIG. 6, which is a cross-sectional view of the charactertype vertical alignment mode LCD device of FIG. 4 or 5, an upperstructure 1 includes the above-mentioned polarizer 11, and a lowerstructure 2 includes the above-mentioned polarizer 21. Also, a verticalalignment mode liquid crystal layer 3 is interposed between the upperstructure 1 and the lower structure 2.

The upper structure 1 is formed by the polarizer 11, an opticalcompensation plate 12, a glass substrate 13, a transparent segmentelectrode layer 14, an insulating layer 15 and a vertical alignmentlayer 16. Similarly, a lower structure 2 is formed by the polarizer 21,an optical compensation plate 22, a glass substrate 23, a transparentcommon electrode layer 24, the above-mentioned grid-shaped wall layerW1, an insulating layer 25 and a vertical alignment layer 26.

The segment electrode layer 14 forms the segment electrodes SEG1, SEG2,. . . , SEG13 of FIG. 1, and the common electrode layer 24 forms thecommon electrodes COM1, COM2, . . . , COM6 of FIG. 2.

The polarizers 11 and 21 are made of iodine-including material ordye-including material such as SHC-13U (trademark) by Polatechno, Japan.The polarizers 11 and 21 cross at 90°. In this case, the angles of thepolarizers 11 and 21 are +45° and −45°, respectively, with respect tothe set director of liquid crystal of the vertical alignment mode liquidcrystal layer 3 to form a crossed Nicols combination, so that a changeof the difference in phase while applying a voltage thereto is maximum.Note that the crossing angle of the polarizers 11 and 21 may be deviatedby a few degrees from 90°. The director of liquid crystal is in an upperdirection (12 o'clock direction) or in a lower direction (6 o'clockdirection) viewed from the top, thus obtaining a broad viewing anglerepresentation having symmetrical viewing angle properties.

Each of the optical compensation plates 12 and 22 is a uniaxialretardation plate which is constructed by a so-called negative C-platewhere the in-plane retardation value ΔR_(e) is 0 nm and the thicknessdirection retardation value ΔR_(th) is 220 nm. An A-plate or a biaxialretardation plate called a B-plate may be used instead of the C-plate.

The transparent segment electrode layer 14 and the transparent commonelectrode layer 24 are made of indium tin oxide (ITO) or the like.

The insulating layers 15 and 25 are used for electrically-isolating thetransparent segment electrode layer 14 and the transparent commonelectrode layer 24, respectively, so as to prevent a short-circuitedstate between the electrode layers 14 and 24 due to a foreign substancewithin the vertical alignment mode liquid crystal layer 3.

The vertical alignment layers 16 and 26 are made of polyimide orinorganic material. The alignment treatment of the vertical alignmentlayers 16 and 26 is carried out by a protrusion alignment process, arubbing alignment process or an ultraviolet ray alignment process. Forexample, a polyimide layer is coated thereon by a flexographic printingprocess and then is cured. Then, a rubbing alignment process is carriedout to give a pretilt angle θ_(p) of 89.5° or 89.9°. In this case, thedirection of the pretilt angle of the vertical alignment layer 26 is 90°in the counterclockwise rotation with respect to the right direction(=0°), while the direction of the pretilt angle of the verticalalignment layer 16 is 90° in the clockwise rotation with respect to theright Direction (=0°), thus realizing an anti-parallel alignment.

The vertical alignment mode liquid crystal layer 3 is of a negativemono-domain type where the dielectric anisotropy Δε is −2.6 and theoptical anisotropy Δn is 0.20. The thickness of the vertical alignmentmode liquid crystal layer 3 is about 2.0 μm. A chiral agent can be addedto the vertical alignment mode liquid crystal layer 3 to avoid thereverse twist phenomenon, thereby realizing a twist structure.

The grid-shaped wall layer W1 has about 50 μm wide wall layers at aninterval (pitch) of about 435 μm on the transparent common electrodelayer 24 and the glass substrate 23. Also, a height H of the grid-shapedwall layer W1 is

H≧T/2

where T is a thickness of the vertical alignment mode liquid crystallayer 3, for example, about 2 μm. Note that thicknesses of the electrodelayers 14 and 24, the insulating layers 15 and 25 and the verticalalignment layers 16 and 26 are much smaller than the thickness T of thevertical alignment mode liquid crystal layer 3; however, thesethicknesses are exaggeratedly illustrated for better understanding.

The grid-shaped wall layer W1 is transparent. However, the grid-shapedwall layer W1 can be opaque (black matrix) in order to maintain thesharpness even if the viewing angle is changed.

The grid-shaped wall layer W1 is formed as follows. For example, anabout 1 μm thick ultraviolet ray hardening resin is coated by a spincoater, and then, the ultraviolet ray hardening resin is temporarilydried. Then, the ultraviolet ray hardening resin is patterned by anultraviolet ray photolithography process using a grid-shaped patternedphotomask. If the grid-shaped wall layer W1 is opaque, carbon or severalkinds of pigments may be included as black material in the ultravioletray hardening resin. Also, since the grid-shaped wall layer W1 is formeddirectly on the common electrode layer 24 forming the common electrodesCOM1, COM2, . . . , COM6, the grid-shaped wall layer W1 generally needsto be made of electrically-insulating material whose resistance value islarger than 10⁹ Ωm. Therefore, the above-mentioned carbon is insulatingcarbon. However, the above-mentioned carbon does not need to beinsulating carbon due to the presence of the insulating layer 25. Notethat, if the grid-shaped wall layer W1 is opaque, the line-width of thegrid-shaped wall layer W1 should be as small as possible, i.e., about 50μm to minimize the reduction of the aperture ratio.

The experimental results of the character type vertical alignment modeLCD device of FIGS. 4 (5) and 6 driven by using the B-waveform at a 1/64duty ratio and a bias of 1/9 are illustrated in FIG. 7.

As illustrated in FIG. 7(A), when θ_(p)=89.5°, black shadow regionscaused by the DMA phenomenon were visible at 330 Hz or less, while noblack shadow regions were visible at 360 Hz or more, to realize anexcellent transmission state of white dots.

Also, as illustrated in FIG. 7(B), when the prior art character typevertical alignment mode LCD device with no grid-shaped wall layer wasdriven under the same conditions as in FIG. 7(A), black shadow regionscaused by the DMA phenomenon were visible at 450 Hz or less, while noblack shadow regions were visible at 480 Hz or more, to realize anexcellent transmission state of white dots.

Thus, the DMA phenomenon was also clearly suppressed as compared withthe prior art character type vertical alignment mode LCD device with nogrid-shaped wall layer.

Note that, when θ_(p)=89.5°, if the thickness T of the verticalalignment mode liquid crystal layer 3 is 4 μm and the height H of thegrid-shaped wall layer W1 is 2 μm (H=T/2), the DMA phenomenon was alsosuppressed. However, if the thickness T of the vertical alignment modeliquid crystal layer 3 was 4 μm and the height H of the grid-shaped walllayer W1 was 1 μm (H=T/4), the DMA phenomenon was not suppressed.

In more detail, as illustrated in FIG. 8 where θ_(p)=89.9°, in order tosuppress the DMA phenomenon, the following is satisfied:

H≧T/2.

As illustrated in FIG. 8(A), when the thickness T of the verticalalignment mode liquid crystal layer 3 was 2 μm and the height H of thegrid-shaped wall layer W1 was 0.7 μm (H/T=0.35), black shadow regionscaused by the DMA phenomenon was visible even at 390 Hz. Therefore, theDMA phenomenon was not so suppressed as compared with the case whereH=T/2 as illustrated in FIG. 8(B).

As illustrated in FIG. 8(C), when the thickness T of the verticalalignment mode liquid crystal layer 3 was 2 μm and the height H of thegrid-shaped wall layer W1 was 1.2 μm (H/T=0.60), black shadow regionscaused by the DMA phenomenon were visible at 330 Hz, while no blackshadow regions were visible at 360 Hz or more. The DMA phenomenon was sosuppressed as compared with the case where H=T/2 as illustrated in FIG.8(B).

Thus, in order to suppress the DMA phenomenon, the following issatisfied:

H≧T/2.

In this case, if H=T, it is impossible to move liquid crystal betweenthe upper structure 1 and the lower structure 2 during a liquid crystalvacuum injecting process for forming the vertical alignment mode liquidcrystal layer 3. Thus, in view of this, the following is satisfied:

H≦0.9T.

However, if a liquid crystal dropping process is used for forming thevertical alignment mode liquid crystal layer 3, where the liquid crystaldropping interval (pitch) is smaller than the interval (pitch) of thewall layers of the grid-shaped wall layer W1, H=T creates no problem. Ofcourse, in the case of such a liquid crystal dropping process where theliquid crystal dropping interval (pitch) is not smaller than theinterval (pitch) of the wall layers of the grid-shaped wall layer W1,the above-mentioned condition, i. e. , H≦0.9 T should be satisfied inthe same way as in a liquid crystal vacuum injecting process.

In the character type vertical alignment mode LCD device of FIGS. 4 (5)and 6, the interval of the wall layers of the grid-shaped wall layer W1can be larger than 435 μm, i.e., 870 μm, 1305 μm and 1740 μm. Note thatthe intervals 870 μm, 1305 μm and 1740 μm of the wall layers correspondto wall layer's spacings 820 μm, 1255 μm and 1690 μm, respectively. Inthis case, the larger the interval of the wall layers, the less thesuppressing effect of the DMA phenomenon. For example, when the intervalof the wall layers was 870 μm or more, no black shadow regions werevisible at 420 Hz or more. Therefore, the interval of the wall layersshould be 400 μm or less.

On the other hand, since liquid crystal at the grid-shaped wall layer W1does not move, the transmittivity while applying a voltage thereto isreduced, i.e., the aperture ratio is reduced. Therefore, the smaller theinterval (pitch) of the wall layers of the grid-shaped wall layer W1,the larger the ratio of the grid-shaped wall layer W1 to the displaypatterns, i. e., the smaller the aperture ratio. In order to suppressthe reduction of the aperture ratio, the line-width of the grid-shapedwall layer W1 is as small as possible; however, a minimum value of theline-width of the grid-shaped wall layer W1 is about 10 μm in view of aphotolithography process for forming the grid-shaped wall layer W1.

Instead of the grid-shaped wall layer W1 provided on the side of thecommon electrode layer 24 as illustrated in FIG. 6, a grid-shaped walllayer W1′ can be provided on the side of the segment electrode layer 14as illustrated in FIG. 9, thus exhibiting the same suppressing effect ofthe DMA phenomenon.

Further, in addition to the grid-shaped wall layer W1 provided on theside of the common electrode layer 24 as illustrated in FIG. 6, agrid-shaped wall layer W1′ can be provided on the side of the segmentelectrode layer 14 as illustrated in FIG. 10, thus exhibiting the samesuppressing effect of the DMA phenomenon. In this case, the height H ofthe grid-shaped wall layer W1 plus the height H′ of the grid-shaped walllayer W1′ is not smaller than half of the thickness T of the verticalalignment mode liquid crystal layer 3, i.e.,

H+H′≧T/2.

However, if H+H′=T, it is impossible to move liquid crystal between theupper structure 1 and the lower structure 2 during a liquid crystalvacuum injecting process for forming the vertical alignment mode liquidcrystal layer 3. Therefore, in view of this, the following should besatisfied:

H+H′≦0.9T.

Note that H+H′=T may be satisfied if a liquid crystal dropping processis used.

In this case, since the grid-shaped wall layers are provided on bothsides of the segment electrode layer 14 and the common electrode layer24 so that the height of each grid-shaped wall layer can be decreased,the portions of the vertical alignment layers 16 and 26 on the sidewallsof the grid-shaped wall layers, which portions are not subject to arubbing alignment process, can be decreased. As a result, the directorof liquid crystal within the dot is less affected by the grid-shapedwall layer.

Also, in the above-described first embodiment, when the grid-shaped walllayers are provided both on the side of the common electrode layer 24and on the side of the segment electrode layer 14, the grid-shaped walllayer on one side can be transparent and the grid-shaped wall layer onthe other side can be opaque (black matrix).

In FIG. 11, which illustrates a second embodiment of the character typevertical alignment mode LCD device according to the presently disclosedsubject matter, wall layers W2 are added to the elements of the priorart character type vertical alignment mode LCD device of FIGS. 1, 2 and3. Even in FIG. 11, note that the display patterns of FIG. 3 isillustrated, but the segment electrodes SEG1, SEG2, . . . , SEG13 ofFIG. 1 and the common electrodes COM1, COM2, . . . , COM6 of FIG. 2 areomitted.

Each of the wall layers W2 has a shape along a periphery of thesmall-sized display pattern P1 or along a periphery of the large-sizeddisplay pattern P2, to thereby suppress the DMA phenomenon caused by anoblique electric field at the small-sized display pattern P1 and thelarge-sized display pattern P2, and also suppress the propagation of theDMA phenomenon.

Referring to FIG. 12, which is a cross-sectional view of the charactertype vertical alignment mode LCD device of FIG. 11, the wall layers W2are about 50 μm wide and are on the transparent common electrode layer24 and the glass substrate 23. Also, a height H of the wall layers W2 is

H≧T/2.

FIG. 13 is a microscopic picture diagram illustrating a first example ofactual wall layers W2 of FIG. 11. In more detail, (A) illustratessegment electrodes SELi and SELi+1 viewed from the bottom of the upperstructure 1, and (B) illustrates common electrodes COMj and COMj+1 andthe wall layers W2 viewed from the top of the lower structure 2. Thesegment electrodes SELi and SELi+1 of FIG. 13(A) are superposed inreverse onto the common electrodes COMj and COMj+1 of (B) of FIG. 13(B).

FIG. 14 is a microscopic picture diagram illustrating a second exampleof actual wall layers W2 of FIG. 11. In more detail, (A) illustratessegment electrodes SELi and SELi+1 viewed from the bottom of the upperstructure 1, and (B) illustrates common electrodes COMj and COMj+1 andthe wall layers W2 viewed from the top of the lower structure 2. Thesegment electrodes SELi and SELi+1 of FIG. 14(A) are superposed inreverse onto the common electrodes COMj and COMj of (B) of FIG. 14(B).

The experimental results of the small-sized display pattern P1 of thecharacter type vertical alignment mode LCD device of FIGS. 11 and 12driven by using the B-waveform at a 1/64 duty ratio and a bias of 1/9are illustrated in FIG. 15.

As illustrated in FIG. 15(A), when θ_(p)=89.5°, black shadow regionscaused by the DMA phenomenon were visible around the wall layers W2 at450 Hz or less, black shadow regions caused by the DMA phenomenonpropagated from one wall layer to one entire pattern unit at 420 Hz orless, and black shadow regions caused by the DMA phenomenon propagatedfrom one pattern unit to its adjacent pattern unit at 330 Hz or less. Onthe other hand, no black shadow regions were visible at 480 Hz or more,to realize an excellent transmission state of white dots.

Also, as illustrated in FIG. 15(B), when the prior art character typevertical alignment mode LCD device with no wall layer driven by the sameconditions as in FIG. 15(A), black shadow regions caused by the DMAphenomenon were visible at 570 Hz or less, black shadow regions causedby the DMA phenomenon propagated from one wall layer to one entirepattern unit at 480 Hz or less, and black shadow regions caused by theDMA phenomenon propagated from one pattern unit to its adjacent patternunit at 450 Hz or less. On the other hand, no black shadow regions werevisible at 600 Hz or more, to realize an excellent transmission state ofwhite dots.

Thus, since a frequency for realizing a stable alignment state was lowerin FIG. 15(A) than in FIG. 15(B), the DMA phenomenon was also clearlysuppressed as compared with the prior art character type verticalalignment mode LCD device with no wall layer. That is, the wall layersW2 have the same shape as the periphery of the display pattern unitsincluding edges of the segment elements or the common electrodes,thereby to suppress the effect of oblique electric fields at the edgesof the segment electrodes or the common electrodes. As a result,generation of the DMA phenomenon can be suppressed, and propagation ofthe DMA phenomenon within one display pattern unit or to its adjacentdisplay pattern unit can be suppressed.

Note that, when θ_(p)=89.5°, if the thickness T of the verticalalignment mode liquid crystal layer 3 was 4 μm and the height H of thewall layers W2 was 2 μm (H=T/2), the DMA phenomenon was also suppressed.However, if the thickness T of the vertical alignment mode liquidcrystal layer 3 was 4 μm and the height H of the wall layers W2 was 1 μm(H=T/4), the DMA phenomenon was not suppressed.

In more detail, in order to suppress the DMA phenomenon, the followingis satisfied:

H≧T/2.

For example, when the thickness T of the vertical alignment mode liquidcrystal layer 3 was 2 μm and the height H of the wall layers W2 was 0.7μm (H/T=0.35), black shadow regions caused by the DMA phenomenon werevisible even at 390 Hz. Therefore, the DMA phenomenon was not sosuppressed as compared with the case where H=T/2.

Also, when the thickness T of the vertical alignment mode liquid crystallayer 3 was 2 μm and the height H of the wall layers W2 was 1.2 μm(H/T=0.60), black shadow regions caused by the DMA phenomenon werevisible at 360 Hz, while no black shadow regions were visible at 390 Hzor more. The DMA phenomenon was more suppressed as compared with thecase where H=T/2.

Thus, in order to suppress the DMA phenomenon, the following issatisfied:

H≧T/2.

Even in this case, if H=T, it is impossible to move liquid crystalbetween the upper structure 1 and the lower structure 2 during a liquidcrystal vacuum injecting process for forming the vertical alignment modeliquid crystal layer 3. Thus, in view of this, the following issatisfied:

H≦0.9T.

However, if a liquid crystal dropping process is used for forming thevertical alignment mode liquid crystal layer 3, where the liquid crystaldropping interval (pitch) is smaller than the interval (pitch) of thewall layers of b the wall layers W2, H=T creates no problem. Of course,in the case of such a liquid crystal dropping process where the liquidcrystal dropping interval (pitch) is not smaller than the interval(pitch) of the wall layers of the wall layers W2, the above-mentionedcondition, i. e., H≦0.9T should be satisfied in the same way as in aliquid crystal vacuum injecting process.

The experimental results of the character type vertical alignment modeLCD device of FIGS. 11 and 12 driven by using the B-waveform at a 1/64duty ratio and a bias of 1/9 are also illustrated in FIG. 16.

As illustrated in FIG. 16(A), which illustrates the small-sized displaypattern P1 whose line-width is about 0. 4 mm, no black shadow regionswere visible at 360 Hz or more, to realize an excellent transmissionstate of white dots.

On the other hand, as illustrated in FIG. 16(B), which illustrates thelarge-sized pattern P2 whose line-width was about 0.8 mm, no blackshadow regions were visible at 450 Hz or more, to realize an excellenttransmission state of white dots.

Thus, the spacing between the wall layers W2 should be 400 μm or less.

In FIG. 17, which illustrates a modification of the character typevertical alignment mode LCD device of FIG. 11, additional wall layers Wrhaving reduced shapes of the wall layers W2 are added to the large-sizedpattern P2. As a result, even in the large-sized pattern P2, the spacingbetween the wall layers W2 and the additional wall layers Wr is 400 μmor less. Therefore, the visibility while applying a voltage is the samein the large-sized pattern P2 as in the small-sized pattern P1.

The cross-sectional view of the large-sized pattern P2 of the charactertype vertical alignment mode LCD device of FIG. 17 is illustrated inFIG. 18.

On the other hand, since liquid crystal at the grid-shaped wall layersW2 and Wr does not move, the transmittivity while applying a voltagethereto is reduced, i.e., the aperture ratio is reduced. Therefore, thesmaller the spacing between the wall layers W2 and Wr, the larger theratio of the wall layers W2 and Wr to the display patterns, i. e., thesmaller the aperture ratio. In order to suppress the reduction of theaperture ratio, the line-width of the wall layers W2 and Wr is as smallas possible; however, a minimum value of the line-width of the walllayers W2 and Wr is about 10 μm in view of a photolithography processfor forming the wall layers W2 and Wr.

Instead of the wall layers W2 provided on the side of the commonelectrode layer 24 as illustrated in FIG. 12 or 18, wall layers W2′ canbe provided on the side of the segment electrode layer 14 as illustratedin FIG. 19, thus exhibiting the same suppressing effect of the DMAphenomenon.

Further, in addition to the wall layers W2 provided on the side of thecommon electrode layer 24 as illustrated in FIG. 12, wall layers W2′ canbe provided on the side of the segment electrode layer 14 as illustratedin FIG. 19, thus exhibiting the same suppressing effect of the DMAphenomenon. In this case, the height H of the wall layers W2 plus theheight H′ of the wall layers W2′ is not smaller than half of thethickness T of the vertical alignment mode liquid crystal layer 3, i.e.,

H+H′≧T/2.

However, if H+H′=T, it is impossible to move liquid crystal between theupper structure 1 and the lower structure 2 during a liquid crystalvacuum injecting process for forming the vertical alignment mode liquidcrystal layer 3. Therefore, in view of this, the following should besatisfied:

H+H′≦0.9 T.

Note that H+H′=T may be satisfied if a liquid crystal dropping processis used.

Even in this case, since the wall layers are provided on both sides ofthe segment electrode layer 14 and the common electrode layer 24 so thatthe height of each of the wall layers can be decreased, the portions ofthe vertical alignment layers 16 and 26 on the sidewalls of the walllayers, which portions are not subject to a rubbing alignment process,can be decreased. As a result, the director of liquid crystal within thedot is less affected by the wall layers.

Also, in the above-described second embodiment, when the wall layers areprovided both on the side of the common electrode layer 24 and on theside of the segment electrode layer 14, the wall layers on one side canbe transparent and the wall layers on the other side can be opaque(black matrix).

The presently disclosed subject matter can be applied to both atransmission-type LCD and a reflection-type LCD. In the case of thereflection-type LCD, a reflective layer can be provided on an outer sideof one of the polarizers, and light can enter and exit at the otherpolarizer.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the presently disclosedsubject matter without departing from the spirit or scope of thepresently disclosed subject matter. Thus, it is intended that thepresently disclosed subject matter covers the modifications andvariations of the presently disclosed subject matter provided they comewithin the scope of the appended claims and their equivalents. Allrelated or prior art references described above and in the Backgroundsection of the present specification are hereby incorporated in theirentirety by reference.

What is claimed is:
 1. A character type vertical alignment mode liquidcrystal display device comprising: first and second substrates opposingeach other; a first electrode layer including a plurality of firstelectrodes provided at an inner side of said first substrate; a secondelectrode layer including a plurality of second electrodes provided atan inner side of said second substrate; first and second verticalalignment layers provided between said first and second substrates tocover said first and second electrode layers, respectively, said firstand second vertical alignment layers being subject to an alignmentprocess from at least one side of said first and second verticalalignment layers; a mono-domain type vertical alignment mode liquidcrystal layer provided between said first and second substrates, one ofsaid first and second alignment layers giving a pretilt angle in liquidcrystal modules in said mono-domain type vertical alignment mode liquidcrystal layer; and a wall structure provided between said first andsecond substrates; wherein said wall structure comprises wall layerseach with a shape along a periphery of one of display patterns formed bysuperposing said segment electrodes onto said common electrodes; andwherein a height of said wall structure is not smaller than half of aheight of said mono-domain type vertical alignment mode liquid crystallayer.
 2. The character type vertical alignment mode liquid crystaldisplay device according to claim 1, wherein said wall structure furthercomprises additional wall layers having reduced shapes of said walllayers.
 3. The character type vertical alignment mode liquid crystaldisplay device according to claim 2, wherein a spacing between said walllayers and said additional wall layers is 400 μm or less.
 4. Thecharacter type vertical alignment mode liquid crystal display deviceaccording to claim 1, wherein said wall structure is provided on a sideof one of said first and second substrates.
 5. The character typevertical alignment mode liquid crystal display device according to claim1, wherein said wall structure is provided on sides of both of saidfirst and second substrates.
 6. The character type vertical alignmentmode liquid crystal display device according to claim 5, wherein a totalheight of said wall structure on the sides of both of said first andsecond substrates is not smaller than half of a height of saidmono-domain type vertical alignment mode liquid crystal layer.
 7. Thecharacter type vertical alignment mode liquid crystal display deviceaccording to claim 1, wherein said first electrodes comprise segmentelectrodes, and said second electrodes comprise common electrodes. 8.The character type vertical alignment mode liquid crystal display deviceaccording to claim 1, wherein said first electrodes comprise commonelectrodes, and said second electrodes comprise segment electrodes. 9.The character type vertical alignment mode liquid crystal display deviceaccording to claim 1, wherein said wall structure comprises ultravioletray hardening resin.